Systems and methods for reducing the particle size of a pozzolan

ABSTRACT

A system for reducing the particle size of a pozzolan includes a thermal fracture system and a defracturing apparatus. The system is highly efficient at drying and heating a natural pozzolan having a natural distribution of particle sizes. The system can create a reduced-size pozzolanic material with a desired particle size and particle morphology. The system for reducing the particle size of a pozzolan includes a thermal fracture system for heating and thermally fracturing the pozzolan and a defracturing apparatus that agitates the thermally fractured pozzolan to break the thermally fractured pozzolan apart.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to apparatus for reducing the particlesize of natural pozzolanic materials.

2. The Relevant Technology

A pozzolan is a material which, when combined with calcium hydroxide,exhibits cementitious properties. Because of its properties, pozzolansare commonly used as an admixture to Portland cement concrete mixturesto increase the long-term strength of the concrete and provide otherbeneficial properties. For example, when added to concrete, pozzolanicmaterials can improve the compressive strength, bond strength, abrasionresistance and other properties of the concrete.

Pozzolans are known to be slower reacting than Portland cement,primarily due to their lower content of tricalcium silicates. When usedin large quantities, pozzolanic material tend to retard early strengthdevelopment. To increase the reactivity of pozzolanic materials,pozzolans can be ground to create smaller pozzolanic particles. Grindinga pozzolan reduces the particle size and increases the surface area,which increases the reactivity of the particles.

To achieve a desired particle size, pozzolans are typically crushed in agrinding mill such as a ball mill. A ball mill is a horizontal cylinderpartly filled with steel balls (or occasionally other shapes) thatrotates on its axis, imparting a tumbling and cascading action to theballs. Material fed through the mill is crushed by impact and ground byattrition between the balls. The grinding media are usually made ofhigh-chromium steel. The smaller grades are occasionally cylindrical(“pebs”) rather than spherical.

BRIEF SUMMARY OF THE INVENTION

The present disclosure provides a system for reducing the particle sizeof a natural pozzolan using thermal fracturing. The system is highlyefficient at drying and heating a natural pozzolan having a naturaldistribution of particle sizes. The system can create reduced-sizepozzolanic material with a desired particle size and particlemorphology. The system for reducing the particle size of a pozzolanincludes a thermal fracture system for heating and thermally fracturingthe pozzolan and a defracturing apparatus that agitates the thermallyfractured pozzolan to break the thermally fractured pozzolan apart.

The thermal fracture system is configured to operate at temperature thatwill thermally fracture the pozzolan, which is a higher temperature thana dryer configured to simply dry a pozzolan. For example, the thermalfracture system can be configured to heat the pozzolan to a temperaturein a range from about 220° F. to about 625° F.

In one embodiment, the thermal fracture system can be configured toretain smaller pozzolanic particles in the dryer for a shorter period oftime than larger pozzolanic particles, on average. Retaining the largerparticle in the dryer for a short period of time allows the largerparticles to absorb more heat and reach the same temperature or even ahigher temperature than the smaller pozzolanic particles. Thus, thesystem can fracture different sized pozzolanic particles to differentextents so as to create a desired distribution of particles sizes (e.g.,fracture larger particles more than smaller particles).

In one embodiment, the dryer used in the thermal fracture system is adrum dryer and the drum dryer can be set on an incline such thatpozzolanic material flowing down the feed path is accelerated down thegrade by gravity. The removal of the pozzolanic particles from the drumdryer can be controlled using a counter-flow of hot air. Pozzolanicparticles flowing down the grade will be retained longer in the drumdryer if they are heavier and have more mass. Thus, heavier more massiveparticles flow through the dryer longer than lighter particles which areswept out of the dryer by the counter flow of hot air. Thus, less heatis expended on the smaller particles since the smaller particles are inthe dryer for a shorter period of time.

In one embodiment, the dryer separates an incoming pozzolanic streaminto at least a coarse fraction and a fine fraction and the coarsefraction is allowed to travel the entire length of the dryer and thecoarse fraction is exposed to higher temperatures compared to the finefraction. Allowing a portion of the pozzolanic material to flow all theway through the dryer allows a coarse portion of the incoming pozzolanicmaterial to be heated to a maximum extent without subjecting the smallparticles to the same heating. For example, the air flow rate can beconfigured to allow less than 50% of the coarse fraction to pass throughthe dryer. In a preferred embodiment, the coarse material passingthrough the dryer (i.e., maximally heated) is in a range from about 0.5%to about 20%, more preferably about 1% to about 10%.

In a preferred embodiment, the dryer is operated using a lighthydrocarbon fuel such as natural gas. Light hydrocarbon fuels such asnatural have been found to limit the amount of carbon in thereduced-size pozzolanic material, which is advantageous for using thepozzolan in concrete manufacturing.

The defracturing system is configured to break apart the thermallyfractured pozzolan to yield a reduced-size pozzolanic material. Thedefracturing system can include an agitation material (i.e., tumblers)that assists in breaking up the thermally fractured material.

The agitation causes the thermally fractured pozzolans to break apart atfracture sites created by the thermal fracturing. The defracturingsystem is configured to agitate as opposed to crush or grind. It hasbeen found that crushing or grinding the pozzolan creates shards thatreduces the flowability of the pozzolanic material. In contrast,agitating the pozzolanic material according to the invention breaksapart the thermally fractured pozzolan into globular particles, which isa desired morphology for using the pozzolanic material to manufactureconcrete.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 discloses a flowchart representing a method for reducing theparticle size of a pozzolan in accordance with an implementation of thepresent invention;

FIG. 2 discloses a schematic representation of an example thermalfracture system of a particle size reducing apparatus in accordance withan implementation of the present invention;

FIG. 3 discloses a schematic representation of an example defracturingsystem of a particle size reducing apparatus in accordance with animplementation of the present invention;

FIG. 4 discloses an example embodiment of the thermal fracture system ofFIG. 2; and

FIG. 5 discloses an example embodiment of the defracturing system ofFIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

The present invention relates to natural pozzolanic materials withreduced particle sizes, as well as methods, systems, and apparatuses formaking the same. Natural pozzolanic materials can provide a number ofbenefits when added to Portland cement concrete mixtures. In particular,natural pozzolanic materials can contribute to increased workability andcompressive strength as well as other improved mechanical properties ofthe concrete mixture.

As found in natural deposits, natural pozzolanic material typically haveparticle sizes that are too large and/or irregular for the naturalpozzolanic material to be feasibly used in a concrete mixture. As aresult, natural pozzolanic materials are often subjected to grinding,crushing, and/or pulverizing processes in order to reduce the particlesizes and allow the natural pozzolanic material to be used in concretemixtures. However, these common methods of reducing the particle sizesof natural pozzolanic materials may produce irregular, highly angular,and/or shard-like particles that increase the water demand and diminishthe workability and other characteristics of concrete mixtures in whichthe natural pozzolanic materials are used.

Accordingly, the present disclosure provides an improved naturalpozzolanic material with reduced particle sizes as well as methods,systems, and apparatuses for reducing the particle size of a naturalpozzolanic material. In particular, the methods, systems, andapparatuses disclosed herein allow the particle size of the naturalpozzolanic material to be reduced without compromising the correspondingworkability, water demand, compressive strength, and other properties ofconcrete mixtures in which the natural pozzolanic material is added.

II. Methods of Reducing the Particle Size of a Pozzolan

FIG. 1 discloses a method 100 for reducing the particle size of apozzolanic material according to the present invention and can bebroadly summarized as follows. First, a natural pozzolanic material isselected 102, wherein the particles of the selected natural pozzolanicmaterial each have an initial particle size. The selected pozzolanicmaterial is then heated to cause a portion of the particles of theselected pozzolanic material to partially fracture 104, thereby creatinga plurality of fissures in the particles to define sub-particles. Thepozzolanic material can then be processed to separate the sub-particlesalong the fissures 106, thereby yielding a pozzolanic material withreduced-sized particles.

A. Natural Pozzolan

A first step of an example method for reducing the particle size of anatural pozzolan includes selecting a natural pozzolanic material. Asused herein, the term “natural pozzolanic material” refers to pozzolanicmaterial originating from naturally occurring pozzolan deposits, such asvolcanic ash deposits. In one embodiment, the natural pozzolanicmaterial can be mined from a natural deposit. The term “naturalpozzolanic material” does not include fly ash, silica fume, metakaolin,or ground granulated blast furnace slag.

The selected natural pozzolanic material includes a plurality ofpozzolanic particles, each having an initial particle size. The initialparticle size of the pozzolanic particles can be any size found in anatural pozzolanic material. Typical examples of particle sizes fornatural pozzolanic materials include deposits with an average particlesize in a range from about 40 microns to 120 microns or alternatively ina range from 60 microns to 90 microns.

The natural pozzolan can be any natural pozzolan that has a particlesize larger than that desired for use in concrete and that can bethermally fractured. Examples of suitable types of natural pozzolansinclude any volcanic ash such as, but not limited to, perlite, tuft, andbasalt. Deposits of these pozzolanic materials can be found throughoutvarious parts of the world. Moreover, those skilled in the art arefamiliar with techniques for extracting natural pozzolanic materialsfrom deposits using known mining techniques.

Typically, it can be advantageous to initially have at least somemoisture in the natural pozzolan so as to facilitate thermal fracturing.Most, if not all, naturally occurring pozzolans have some moisturecontent and often times, the amount is somewhat constant throughout thenatural deposit of pozzolan. When used in the process of the presentinvention, the selected pozzolanic material may have an initial moisturecontent similar to the natural deposit or may have a moisture contentthat is less or greater than the natural pozzolan. In other words,moisture can be added to the pozzolan or the pozzolan can be dried toensure a desired and/or consistent moisture content. In one embodiment,the moisture content of the pozzolan at the outset of the method forreducing the particle size is in a range from about 4% by weight toabout 16% by weight.

B. Heating the Natural Pozzolan

As mentioned, a subsequent step of the method of reducing the particlesize of a pozzolan includes heating the selected pozzolanic material tocause a portion of the particles of the selected pozzolanic material tofracture. In one embodiment, the temperature to which the pozzolanicmaterial is heated is preferably sufficient to fracture at least aportion of the particles of the pozzolanic material. This temperature isreferred to herein as a “fracture temperature” or “thermal fracturetemperature”.

The thermal fracture temperature can be varied to achieve a desiredparticle size. In general, for a given pozzolanic material and moisturecontent, a higher thermal fracture temperature will result in smallerparticles and lower thermal fracture temperatures results in largerparticles. In one embodiment, the thermal fracture temperature can be ina range from about 2200 Fahrenheit to about 6250 Fahrenheit, preferablyfrom about 2500 Fahrenheit to about 5000 Fahrenheit, more preferablyfrom about 3000 Fahrenheit to about 4500 Fahrenheit and most preferablyfrom about 3500 Fahrenheit to about 4000 Fahrenheit. In one exampleembodiment, the fracture temperature can be about 3750 Fahrenheit.

By heating the pozzolanic material, the pozzolanic particles can bethermally fractured. Causing the particles to fracture can create aplurality of fissures (or thermal fracture lines) in the particles thatdefine sub-particles of the fractured particles. The thermal fracture ofthe particles may result from the expansion of moisture trapped withinthe particles. For example, each pozzolanic particle can contain acertain amount of moisture in voids within the particle. As the watertrapped within the particle is heated past the boiling point, it canturn into pressurized steam. The pressure of the steam can continue toincrease as its heat rises until the particle reaches a breaking point.The particle may at least partially rupture, thereby releasing thepressurized steam. The particle may either partially fracture along oneor more fissures defining sub-particles, or the particle may entirelyfracture along one or more fissures and separate into one or moresub-particles. In one example embodiment, the pozzolanic material can beheated to cause more than about 25% of the particles to fracture, morepreferably more than about 50% of the particles, and most preferablymore than about 75% of the particles.

It has been found that by thermally fracturing the particles of thepozzolanic material into sub-particles, a desired shape of thesub-particles can be achieved. For example, it is believed that thethermal fracture process described herein fractures the pozzolanicparticles along natural fracture lines which define sub-particles havinga more regular shape than is produced by physically or mechanicallyfracturing the particles, such as by pulverizing or crushing, whichresults in more jagged or shard-like particles. In one exampleembodiment, the resulting sub-particles can have a substantiallyspheroidal shape. As used herein, “spheroidal” includes spherical,approximately spherical, round, approximately round, rounded, ballshaped, clump shaped, globular, orbicular, and/or similar shapes.

C. Processing the Natural Pozzolan

Once heated to fracture a portion of the particles, the pozzolanicmaterial can then be processed in order to separate the particles alongthe fracture line into sub-particles. Processing the pozzolanic materialcan thereby yield a pozzolanic material having reduced particle sizes.

Processing the thermally fractured particles can include, but is notlimited to, milling, tumbling, vibrating, agitating, stirring, shaking,air classifying, and/or other similar procedures. It may be importantthat processing the pozzolanic material does introduce a significantamount of physical or mechanical fractures in the pozzolanic particles,such as by grinding, crushing, and/or pulverizing. In one exampleembodiment, processing the pozzolanic particles introduces physical ormechanical fractures in less than about 50% of the particles, morepreferably in less than about 30% of the particles, and most preferablyin less than about 15% of the particles.

The resulting pozzolanic material will have smaller particles thanbefore the pozzolanic material was heated to a thermal fracturetemperature and then processed. In one example embodiment, at leastabout 95% by volume of the particles of the resulting pozzolanicmaterial have a diameter smaller than about 50 microns, more preferablysmaller than about 40 microns, and most preferably smaller than about 38microns. In an additional configuration, at least about 99% of theparticles have a diameter smaller than about 38 microns.

The median size of the particles of the resulting pozzolanic materialcan also be reduced. For example, in one configuration, the median sizeof the pozzolanic particles ranges from about 1 micron to about 25microns, more preferably from about 3 microns to about 15 microns, andmost preferably from about 6 microns to about 10 microns.

In a further embodiment, additional steps may be taken to further reducethe particle size of the resulting pozzolanic material. For example, theparticles of the pozzolanic material may be separated based on particlesize, such as by using an air classifier. Particles having a particlesize greater than a desired particle size may be removed and thenfurther fractured and/or processed until a desired particle size isachieved. Alternatively, these particles may be discarded.

The resulting pozzolanic material with reduced-size particles can havemoisture content less than before thermal fracture and processing. Inone example embodiment, the resulting pozzolanic material withreduced-size particles has a moisture content of less than about 4% byvolume, more preferably less than about 2% by volume, and mostpreferably less than about 1% by volume.

The resulting pozzolanic material may also have relatively low carboncontent. For example, the carbon content of the resulting pozzolanicmaterial can be less about 4% by volume, more preferably less than about2% by volume, and most preferably less than about 1% by volume.

The substantially spheroidal shape of the particles of the resultingpozzolanic material can reduce the friction between multiple pozzolanicparticles and/or between the pozzolanic particles and other particles ofa cement or concrete mixture. Accordingly, the resulting pozzolanicmaterial can reduce the water demand and enhance the workability ofcement or concrete mixture. In addition, the pozzolanic material of thepresent invention can improve other characteristics and properties of acement or concrete mixture in which the pozzolanic material is added.

III. Natural Pozzolanic Materials with Reduced Particle Sizes

The pozzolanic materials of the present invention have reduced-sizeparticles compared to the natural deposit from which the naturalpozzolan originated from. In addition, the methods used to reduce theparticle size produces a natural pozzolan with a substantiallyspheroidal shape. For purposes of this invention, the term substantiallyspheroidal means “sphere-like” or “globular” as opposed to shard-like.Nevertheless, because the pozzolans are fractured along natural crystalplanes, very few, if any, of the particles are perfectly round.

As a result of their substantially spheroidal shape, the pozzolanicmaterials can improve the workability of a cement paste or concretemixture by reducing the friction between particles within a cement pasteor concrete mixture (as compared to pozzolanic particles that arecrushed). In addition, the pozzolanic materials of the present inventioncan improve other characteristics and properties of a cement paste orconcrete mixture in which the pozzolanic materials are added.

The pozzolanic materials of the present invention can have desirablysmall particle sizes. In one example embodiment, at least about 95% ofthe particles by volume have a diameter smaller than about 50 microns,more preferably smaller than about 40 microns, and most preferablysmaller than about 38 microns. In an additional configuration, at leastabout 99% of the particles have a diameter smaller than about 38microns.

The median size of the particles of the pozzolanic material of thepresent invention can also be desirably small. For example, the mediansize of the particles of the pozzolanic material of the presentinvention can range from about 1 micron to about 25 microns, morepreferably from about 6 microns to about 15 microns, and most preferablyfrom about 8 microns to about 12 microns.

The moisture content of the pozzolanic material of the present inventioncan be less than other natural pozzolanic materials. In particular, inone example embodiment, the water content of the reduced sizedpozzolanic material can be less than about 4% by volume, more preferablyless than about 2% by volume, and most preferably less than about 1% byvolume.

The carbon content of the pozzolanic material of the present inventionmay also be less than other pozzolanic materials (e.g., less than flyash). For example, the carbon content of the pozzolanic material can beless than about 4% by volume, more preferably less than about 2% byvolume, and most preferably less than about 1% by volume, or evensubstantially free of carbon.

The reduced-size particles of the pozzolanic material can have asubstantially spheroidal shape with more rounded and/or regular shapes.In contrast, particles being reduced in size by grinding have angular,jagged, edges that result in a shard-like shape.

The pozzolanic material of the present invention may be included in acement or concrete composition. In particular, the pozzolanic materialdescribed above can be included with Portland cement and water to form acement paste. In a further embodiment, aggregate can be added to thecement paste to form a concrete mixture. As mentioned above, thepozzolanic material of the present invention can improve the physicaland other characteristics of the cement or concrete compositions inwhich the pozzolanic material is added.

For example, the replacement of cement with the pozzolanic material ofthe present invention can reduce the water demand of a concrete mixturefor a given slump. In one example embodiment, when the pozzolanicmaterial of the present invention is Mused as about 20 percent of thetotal cementitious materials of a concrete mixture, the water demand ofthe concrete mixture can be reduced by more than about 5 percent,preferably by more than about 10 percent, for a given slump. In furtherembodiments, higher pozzolanic material contents can yield higher waterreductions. In addition, the pozzolanic material of the presentinvention may improve other characteristics of the concrete mixture,such as compressive strength.

IV. Apparatus for Reducing the Particle Size of a Pozzolan

An apparatus for reducing the particle size of a pozzolan is disclosed.The particle size reducing apparatus may include a thermal fracturesystem and a defracturing system. The thermal fracture system may beconfigured to heat a pozzolanic material to a thermal fracturetemperature, as described above, as well as perform other related steps.The defracturing system may be configured to process the pozzolanicmaterial to break apart fractured particles into sub-particles as wellas perform other related steps. In further embodiments, the particlesize reducing apparatus may also include other systems and/or devices.

In one embodiment, the thermal fracture system can be configured to heatsmaller pozzolanic particles for a shorter period of time than largerpozzolanic particles, and/or heat larger particles at a highertemperature than smaller particles. For example, in one embodiment,larger particles can be selectively retained in a forced-air dryer for alonger period of time than relatively smaller particles to allow thelarger particles to absorb more heat. The additional heat absorbed bythe larger particles can raise the temperature of the larger particlesto a desired thermal fracture temperature. In one embodiment, theadditional heating of the larger pozzolanic particles can cause thelarger particles to undergo more extensive thermal fracturing, which canreduce the particle size of the larger particles more compared tosmaller sized particles. Thus, the system can fracture different sizedpozzolanic particles to different extents so as to create a desireddistribution of particles sizes (e.g., fracture larger particles morethan smaller particles).

FIG. 3 discloses a schematic diagram of a portion of an example particlesize reducing apparatus. In particular, FIG. 3 illustrates an examplethermal fracture system 300. In one embodiment, the thermal fracturesystem 300 can perform one or more of the steps of the methods ofreducing the particle size of a pozzolan as disclosed in more detailabove. In particular, the thermal fracture system 300 may include one ormore components configured to heat a selected pozzolanic material tocause a portion of the pozzolanic particles to partially fracture.

In one embodiment, the thermal fracture system 300 may comprise acylindrical fracture drum 310 that is used to heat the pozzolanicmaterials (e.g., using hot forced air). The fracture drum 310 can bepositioned at an angle 312 from a horizontal position and can beconfigured to rotate about its longitudinal axis 314. The angle 312 ofthe fracture drum 310 with respect to a horizontal position may varyaccording to different configurations. In one example embodiment, theangle 312 can range from about 1° to about 30°.

The fracture drum 310 may have an open upper end 310 a and an open lowerend 310 b. The diameter of the fracture drum 310 may vary as desired fora particular configuration. For example, the diameter of the fracturedrum 310 may range from about 1′ to about 15′. The length of thefracture drum 310 may also vary as desired. In particular, the length ofthe fracture drum 310 can range from about 5′ to about 120′.

Pozzolanic material may be introduced into the upper end 310 a of the °fracture drum 310 through an input 305, such as a hopper. The pozzolanicmaterial may travel toward the lower end 310 b as the fracture drum 310rotates. The pozzolanic material may be tumbled and/or otherwiseagitated as it travels through the rotating fracture drum 310. Inparticular, the fracture drum 310 may include one or more flutes (notshown) on the interior surface of the fracture drum 310 to assist intumbling and/or tossing the pozzolanic material as it travels throughthe fracture drum 310. The rotational speed of the fracture drum 310 canvary depending on a desired configuration. For example, the rotationalspeed of the fracture drum 310 can range from about 10 RPM to about 100RPM, more preferably from about 20 RPM to about 60 RPM, and mostpreferably from about 30 RPM to about 45 RPM.

The thermal fracture system 300 may also include a heating element 320.For example, the heating element 320 may comprise a burner positionedproximate to or at least partially within the fracture drum 310. In oneexample configuration, the heating element 320 can be positionedproximate the lower end 310 b of the fracture drum 310 and can beconfigured to direct heat into the interior cavity of the fracture drum310 from the lower end 310 b towards the upper end 310 a. As a result,pozzolanic material traveling through the fracture drum 310 can beheated to cause a portion of the pozzolanic particles to fracture.

The heating element 320 may produce heat by burning one or morecombustible materials. For example, the heating element 320 may burnmethane, propane, butane, heptane, octane, and the like. In a furtherembodiment, it may be important to use a combustible material with a permolecule carbon atom total equal to or less than about 8 to reduce theamount of carbon atoms adsorbed by the pozzolanic material during thethermal fracture process. In particular, the heating element 320 canburn liquid natural gas or liquid propane. In yet further embodiments,the heating element may produce heat via electricity, microwaves,infrared radiation, ultraviolet lights, and/or other similarheat-producing sources.

The heating element 320 can be configured to heat the pozzolanicmaterial traveling through the fracture drum 310 to a thermal fracturetemperature. For example, the heating element 320 can heat thepozzolanic material to a temperature in the range of about 220°Fahrenheit to about 625° Fahrenheit, preferably from about 250°Fahrenheit to about 500° Fahrenheit, more preferably from about 300°Fahrenheit to about 450° Fahrenheit and most preferably from about 350°Fahrenheit to about 400° Fahrenheit. As explained in more detail above,heating the pozzolanic material can cause at least a portion of thepozzolanic particles to partially fracture into smaller sub-particles.In one example embodiment, heating the pozzolanic material can causemore than about 25% of the pozzolanic particles to at least partiallyfracture, preferably more than about 50%, more preferably more thanabout 75%.

The extent of thermal fracturing will depend in part on the temperatureof the heating element, the duration of the particles in the heatgenerated from the heating element and the proximity of the particles tothe heating element. In general, the closer the particles are to thesource of the heat, the hotter the flame and the hotter the particleswill be heated and thus the more extensive the thermal fracturing willbe.

In general, to increase the flow of pozzolanic material through the drum310, the force of the counter-flowing hot air is reduced and the angle312 of drum 310 is increased. Alternatively, the flow of pozzolanicmaterial through drum 310 can be reduced by decreasing angle 312 and/orincreasing the airflow of hot gases.

In addition to thermally fracturing the pozzolanic material, the thermalfracture system 300 may also reduce the water content of the pozzolanicmaterial. As explained in more detail above, heating pozzolanic materialto a thermal fracture temperature can release moisture trapped withinthe pozzolanic particles. Additional moisture, such as on the surface ofthe particles, may also evaporate as a result of the heat. Consequently,pozzolanic materials exiting the fracture drum 310 can have watercontent less than when the pozzolanic materials were introduced into thethermal fracture system 300. In particular, the water content of thethermally fractured pozzolanic material can be less than about 4% byvolume, preferably less than about 2% by volume, more preferably lessthan about 1% by volume.

In alternative embodiments, the thermal fracture system 300 may alsoinclude any devices and/or components configured to heat the pozzolanicmaterial to a thermal fracture temperature. For example, the thermalfracture system 300 may comprise one or more ovens into which thepozzolanic material may be introduced and heated to a thermal fracturetemperature. In a further embodiment, the thermal fracture system 300may comprise a conveyer belt system combined with one or more heatingelements 320 to heat pozzolanic materials being carried by the conveyerbelt system to a thermal fracture temperature. Furthermore, one willappreciate that additional methods of heating the pozzolanic material toa thermal fracture temperature may be used.

The thermal fracture system 300 may also include one or more elementsfor efficiently heating different sized particles for different amountsof time. For example, the thermal fracture system 300 may include adraft fan 330 that draws a back draft of air flow through the fracturedrum 310 flowing from the lower end 310 b to the upper end 310 a. In oneexample embodiment, the back draft created by the draft fan 330 cancarry smaller, lighter particles within the fracture drum 310 out of theupper end 310 a, while larger, heavier particles continue to travel andtumble through the fracture drum 310 until they become light enough tobe carried by the back draft or until they are discharged out the lowerend 310 b.

A portion of the pozzolanic particles traveling through the fracturedrum 310 can become lighter and/or smaller by being thermally fracturedinto sub-particles and/or by having their water content reduced. As aresult, these particles may become small and light enough to be carriedout the upper end 310 a of the fracture drum 310 by the back draft. Theparticles that do not achieve a small enough size and/or weightnecessary to be carried by the back draft can be discharged through thelower end 310 b. As a result, different sized and shaped particles canbe respectively heated different amounts. In particular, smaller,lighter particles, which require less energy to achieve a thermalfracture temperature, may remain within the fracture drum 310 for only ashort period of time, while larger, heavier particles that require moreenergy to achieve a thermal fracture temperature may remain in thefracture drum 310 for a longer period of time. Accordingly, by removingparticles once they have reached a desired particle size, the thermalfracture system 300 can more efficiently allocate energy used in heatingthe pozzolanic material to the particles that need it most and notoverheat particles that have already achieved a desired particle size.

The amount of heat produced by the heating element 320 and the volume ofair flow generated by the draft fan 330 can be varied as necessary toachieve a desired distribution of heat and energy and to achieve aparticular temperature in each of the particles. In one embodiment, theair flow and fracture temperature are configured such that a majority ofthe particles exit the fracture drum 310 with the back draft created bythe draft fan 330 through the upper end 310 a while a minority of thepozzolanic particles are discharged from the lower end 310 b. The volumeof air flow created by the draft fan 330 can range from about 50 cubicfeet per minute (CFM) to about 450 CFM, more preferably from about 200CFM to about 350 CFM, and most preferably from about 250 CFM to about300 CFM. The air flow and/or temperature may also be varied based on theelevation and/or humidity where the thermal fracture system is located.

Particles carried out the upper end 310 a of the fracture drum 310 bythe back draft can be collected using one or more particle collectiondevices. For example, the back draft can carry the particles from thefracture drum 310 into one or more cyclone dust collectors 340. Thecyclone dust collectors 340 can separate particles out of the back draftthat are larger than a particular size while particles smaller than aparticular size remain suspended within the air flow of the back draft.In one example embodiment, the cyclone dust collectors 340 may collectparticles having a particle size between about 30 microns and about 75microns. Once collected, the particles can be transported to anintermediate storage device 360.

The remaining particles suspended in the air flow of the back draft canbe further collected using one or more baghouses 350. For example, thebaghouse(s) 350 may collect particles that have a particle size of lessthan about 30 microns. Once collected by the baghouse(s) 350, theseparticles may also be transported to the intermediate storage device360.

As mentioned above, particles that are too heavy and/or large to becarried out of the upper end 310 a of the fracture drum 310 by the backdraft may be discharged from the lower end 310 b of the fracture drum310. These particles may be recycled through the fracture drum 310 ormay be transported to the intermediate storage device 360 to be storedwith the other particles.

In one embodiment it can be preferably to set the air-flow and angle ofthe drum such that a majority of the thermally fractured pozzolanicmaterial is collected in the baghouse rather than traveling through theentire drum. Thus, the heating element can have a section of high heatfor fracturing the largest and most difficult to fracture particles,without subjecting the rest of the particles to such high heat, whichcould waste energy and/or over fracture the smaller particles or changetheir chemical properties. In a preferred embodiment, the coarsefraction that enters the hottest zone of drum 310 and/or passes throughdrum 310 to exit end 310 b is about 0.5% to about 20% by weight of thepozzolanic material (after being dried). More preferably the coarsefraction is between about 1% and 10% by weight of the pozzolanicmaterial.

From the immediate storage device 360, the pozzolanic material can beintroduced into a defracturing system 400, as disclosed in FIG. 4. Thedefracturing system 400 may include one or more components configured toseparate the particles into sub-particles defined by thermal fracturelines, thereby yielding a pozzolanic material with reduced-sizeparticles. Upon exiting the defracturing system 400, particles largerthan a desired particle size may be removed and either discarded orrecycled through the thermal fracture system 300 and/or defracturingsystem 400. Particles equal to or smaller than a desired particle sizecan be transported into a final storage device 450.

The defracturing system 400 can comprise one or more devices configuredto agitate the particles and induce separation along thermal fracturelines without introducing a significant amount of new physical ormechanical fracture lines in the particles. Breaking apart the particlesby agitating the particles prevents minimizes the percentage ofparticles that form shards, which is typically the morphology achievedusing traditional grinding techniques to reduce particle size.

In one example embodiment, the defracturing system 400 can comprise aprocessing mill 410. The processing mill 410 may include one or morecylindrical processing drums 415 positioned in parallel and/or inseries. In one example embodiment, the processing mill 410 includes aplurality of processing drums 415 positioned in series coupled end toend. For example, each processing drum 415 can have flanged ends toconnect with the corresponding flanged ends of the subsequent and/orpreceding processing drums 415 in a series, such as by welding, bolting,and/or otherwise. In a further embodiment, the processing mill 410 caninclude a second series of processing drums 415 in parallel with anotherseries of processing drums 415. The length of the processing mill 410can range from about 3′ to about 120′. The diameter of the processingdrums 415 may also vary in size and can range from about 12″ to about120″.

The processing mill 410 may also include one or more baffles 416positioned within or between the processing drums 415 intermittentlyalong the length of the processing mill 410. In one embodiment, thebaffles 416 may be positioned between consecutive processing drums in aseries of processing drums. The baffles 416 may be configured to inhibitand/or regulate the flow of pozzolanic material through the processingmill 410 to ensure that the pozzolanic particles remain in theprocessing mill 410 for sufficient time to properly separate beforebeing discharged from the processing mill 410. Each baffle 416 maycomprise, for example, a plate or screen including a plurality ofapertures for the passage of pozzolanic particles. The size and shape ofthe apertures may vary from baffle 416 to baffle 416 along the length ofthe processing mill 410. The diameter of the apertures may range fromabout ¼″ to about 3″.

The processing mill 410 may also include a plurality of trunions (notshown) to support and facilitate the rotation of the processing mill410. In one example, the processing mill 410 rotates on at least one setof steel barring load rubber wheeled trunions. In addition, theprocessing mill 410 may comprise a motor coupled to the processing mill410 through a gear drive to rotate the processing mill 410. Themotor/gear drive combination may rotate the processing mill 410 at aspeed ranging from about 10 RPM to about 120 RPM, more preferably fromabout 20 RPM to about 90 RPM, and most preferably from about 30 RPM toabout 60 RPM.

The processing mill 410 may also contain one or more tumblers (notshown) configured to prevent the pozzolanic material from adhering tothe inner walls of the processing drum 415 and agitate the thermallyfractured pozzolanic material as it travels through the processing mill.The tumblers can be any solid object large enough to not pass throughthe apertures in the baffles 416. The tumblers can be regular orirregular in shape. For example, the tumblers can have a rod shape,diamond shape, cone shape, polygon shape, spherical shape, spheroidalshape, and/or other similar shapes. In addition, the tumblers caninclude one or more of a variety of materials. For example, the tumblerscan include polyurethanes, polymers, rubbers, synthetic rubber, metals,and/or other similar materials.

In addition—or as an alternative—to tumbling the pozzolanic material,the defracturing system 400 may exert additional forces on thepozzolanic particles to separate the particles along thermal fracturelines or fissures into sub-particles. For example, the defracturingsystem 400 may exert vibrational forces, static electric forces,frictional forces, and/or other similar forces to assist in separatingthe particles into the sub-particles defined by the thermal fracturelines. For example, the processing mill 410 may be vibrated eithercontinuously or intermittently. In a further embodiment, the tumblingaction of the processing mill 410 may create static electrical chargesbetween particles that may assist in separating sub-particles. One willappreciate that additional methods may also be used to separate thefractured particles into sub-particles.

It may be important that the defracturing system 400 not introduceadditional physical or mechanical fractures, such as by pulverizing orcrushing, in the pozzolanic particles in order to maintain thesubstantially spheroidal shape of the sub-particles. In one embodiment,the defracturing system 400 introduces physical or mechanical fracturesin less than about 50% of the pozzolanic particles, more preferably lessthan about 30%, and most preferably less than about 15%.

One way to reduce the amount of fracturing caused by the processing millis to use tumblers (i.e., agitation material) that are substantiallylarger than the particle size of the thermally fractured pozzolan.operate the drum well below the critical speed of rotation. The crushingof particles in a traditional mill is generally accomplished by rotatingthe mill near the critical speed such that the grinding balls willtravel up the wall of the mill and then fall from the roof of the milland crush the pozzolanic material. This grinding action can be avoidedby configuring the defracturing apparatus to operate well below thecritical speed of the mill such that the agitation material does notfall a sufficient distance to cause crushing. In this manner thetumblers used in the system of the invention can agitate withoutgrinding. In one embodiment, the processing mill is a drum that isoperated within about 1% to 50% of the critical speed, more preferablyabout 5% to about 30%. Alternatively, grinding can be minimized by usingagitation material that is relatively soft, such as a hard rubber orother non-metallic material. In addition, the agitation material ispreferably not spherical. In one embodiment, the agitation materialincludes points, prongs, and/or facets (e.g., a material that is shapedlike a jack). In a preferred embodiment, the agitation material has asize in a range from about 0.5 inches to about 6 inches, more preferablyin a range from about 1 inch to about 4 inches.

Once the pozzolanic particles are processed and then discharged from thedefracturing system 400, they can be introduced into a particleseparator 430. For example, particle separator 430 can include one ormore air classifiers to separate the particles based on particle size.As a result, particles having a particle size greater than a desiredparticle size can be separated out of the pozzolanic material and eitherdiscarded or recycled through the thermal fracture system (e.g., 300,FIG. 3) and/or defracturing system 400. In one example embodiment, theparticle separator 430 can separate out particles having a diametergreater than about 50 microns, more preferably greater than about 40microns, and most preferably greater than about 38 microns.

The remaining particles having particle sizes equal to or smaller than adesired particle size can be transported into a final storage device450. One or more baghouses 440 may be used in conjunction with theparticle separator 430 to filter pozzolanic particles from the dischargeof the particle separator 430.

As disclosed above, the thermal fracture system 300 and defracturingsystem 400 may each include one or more baghouses (e.g., 350, FIG. 3;440, FIG. 4). These baghouses 350, 440 may be coupled to one or morebaghouse cleaning systems (not shown), such as a pulse jet system, ashaker system, a reverse air system, similar systems, and/orcombinations of the same. The baghouse cleaning systems can assist inremoving pozzolanic particle accumulations from the baghouses 350, 440,which can then be discarded or transported to the final storage device450.

FIG. 5 illustrates an example embodiment of the thermal fracture systemof FIG. 3. In particular, FIG. 5 discloses a thermal fracture system 500including a fracture drum 510 fed by a conveyer system 505. The examplefracture drum 510 has a length of at least 46′ and a diameter of atleast 9′. The fracture drum 510 can enclose a three million BTU burner(not shown) fueled by Natural Liquid Propane. The fracture drum 510 canfeed into a discharge box 520 and then pass through an Air Lock Starvalve 530 and blown through a 6″ pipe 540 into a 30-ton intermediatestorage silo 550.

From the intermediate storage silo 550, the pozzolanic material cantravel through another Air Lock Star valve 555 and into the defracturingsystem 600 illustrated in FIG. 6. The defracturing system 600 caninclude a processing mill 610 having a length of about 60′ and adiameter of about 48.″ The processing mill 610 can include a series ofsix spool chambers 615 flanged at both ends and bolted together. Thespool chambers 615 can be separated by filter flanges 616 each includinga plurality of holes. The first two filter flanges 616 in the series canhave ¾″ holes while the remaining filter flanges 616 can have ½″ holes.The first two spool chambers 615 can each be filled with 1150 pounds of1½″ A210 hardened steel balls while the remaining spool chambers 615 inthe series can each include 1230 pounds of 1″ A210 hardened steel balls.The processing mill 610 can be driven by a 200 hp 1760 RPM GE 3 phasemotor interlocked with a Walker Thompson 50-to-1 ratio gear drive. Theprocessing mill can be positioned on an eight-percent grade and rotatedat about 46 RPM.

The defracturing system 600 can also include fully-enclosed bucketelevator 620 to transport pozzolanic material from the processing mill610 to an AB1012 30-ton per hour centrifuge air classifier 630 linedwith Alumina Ceramic for abrasion resistance. The air classifier 630 canbe set to reject particles that are not 37 microns or smaller whileparticles that are 37 microns or smaller can be transported through anAirlock Star Valve 635 and into a 6″ pressure line 640, from which theycan be blown into a finish product silo 650.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A system for reducing the particle size of a natural pozzolan,comprising: a source of a pozzolanic material; a thermal fracture systemthat includes a dryer configured to thermally fracture the pozzolanicmaterial; a feed mechanism coupled to the dryer and configured tointroduce the pozzolanic material into the dryer; and a defracturingapparatus configured to agitate the thermally fractured pozzolan so asto break apart the thermally fractured pozzolan into smaller-sizedparticles.
 2. A system as in claim 1, wherein the pozzolanic material isa natural pozzolanic material.
 3. A system as in claim 1, furtherconfigured to retain smaller pozzolanic particles in the dryer for ashorter period of time than larger pozzolanic particles, on average. 4.A system as in claim 3, wherein the dryer is a drum dryer.
 5. A systemas in claim 4, wherein the drum dryer separates an incoming pozzolanicstream into at least a coarse fraction and a fine fraction, wherein thecoarse fraction is exposed to higher temperatures in the dryer comparedto the fine fraction.
 6. A system as in claim 5, wherein thermalfracture system is configured to allow from about 0.5% to about 20% ofthe coarse fraction to pass through a hottest section of the dryer.
 7. Asystem as in claim 5, wherein thermal fracture system is configured toallow from about 1% to about 10% of the coarse fraction to pass througha hottest section of the dryer.
 8. A system as in claim 1, wherein thedryer has a feed path with a grade, the grade allowing gravity toaccelerate at least a portion of the pozzolanic material down the feedpath.
 9. A system as in claim 7, wherein the grade of the feed path isin a range from 2% to 12%.
 10. A system as in claim 8, wherein the dryeris configured to produce air that flows along the feed path against thegrade.
 11. A system as in claim 1, wherein the dryer is a natural gasdryer, the system further comprising a natural gas source coupled to thedryer.
 12. A system as in claim 1, wherein the defracturing apparatus isconfigured to agitate thermally fractured pozzolanic particles so as toyield globular shaped particles for a majority of the reduced-sizeparticles.
 13. A system as in claim 1, wherein the defracturingapparatus includes a plurality of tumblers comprising a non-metallicmaterial.
 14. A system as in claim 1, wherein the non-metallic materialis a polymer, rubber, polyurethane, and/or synthetic rubber.
 15. Asystem as in claim 1, wherein the tumbler has a diameter of at least 1inch.
 16. A method for using an apparatus to reduce the particle size ofa pozzolan, comprising: providing a source of a natural pozzolanicmaterial; providing a dryer suitable for heating the natural pozzolanicmaterial; introducing the pozzolanic material into the dryer and heatingthe pozzolanic material to a thermal fracturing temperature therebythermally fracturing the pozzolanic material; and processing thethermally fractured pozzolan in a defracturing apparatus configured toagitate the thermally fractured pozzolan, so as to yield a reduced-sizepozzolanic material.
 17. A method as in claim 16, wherein the agitationis carried out in a rotating drum.
 18. A method as in claim 15, whereinthe agitation yields reduced-size particles having a substantiallyglobular shape.
 19. A method as in claim 16, wherein the defracturingapparatus includes a plurality of tumblers comprising a non-metallicmaterial.
 20. A method as in claim 19, wherein the non-metallic materialincludes rubber.
 21. A method as in claim 19, wherein the tumblers havea diameter of at least one inch.
 22. A method as in claim 16, whereinthe dryer includes forced-air heating, the forced air having a counterflow to a flow of the pozzolanic material being introduced into thedryer.
 23. A method as in claim 16, wherein smaller pozzolanic particlesare retained in the dryer for a shorter period of time than largerpozzolanic particles, on average.
 24. A method as in claim 16, whereinthe dryer separates an incoming pozzolanic stream into at least a coarsefraction and a fine fraction, wherein the coarse fraction is exposed tohigher temperatures in the dryer compared to the fine fraction.
 25. Amethod as in claim 24, wherein thermal fracture system is configured toallow from about 0.5% to about 20% of the coarse fraction to passthrough a hottest section of the dryer.
 26. A method as in claim 16,further comprising operating the dryer using natural gas.
 27. A methodas in claim 16, wherein the pozzolanic material is heated to atemperature in a range from about 220° F. to about 625° F.